The interest in small interfering, non-coding microRNAs has exploded due to emerging discoveries of their diversity and prevalence across animal species. For all of the enthusiasm that they have garnered in the field, very little is known of their individual target genes and biological functions. The goal of this proposal is to determine the function of a set of microRNAs expressed in the developing vertebrate limb bud by combining molecular biology, computational bioinformatics, and classical embryology. Specific Aim 1 will test the hypothesis that let-7e functions in the limb to inhibit inappropriate chondrogenesis. Specific Aim 2 will use similar experimental methods to investigate the functions of five additional microRNAs expressed strongly in the vertebrate limb. Specific Aim 3 will focus on elucidating the requirement for the microRNA assocated protein Argonaute 2 and its cognate microRNAs by generating a conditional null allele of Ago2 in the mouse and performing a microarray analysis. The results of these investigations will reveal functions of microRNAs in the developing embryo and will open avenues to research that may allow development of antisense RNA technology for therapeutic applications. [unreadable] [unreadable]